<!DOCTYPE html>
<html>
  <head>
    <style>
      span { color: red; }
      :-moz-any(:valid) + span { color: green; }
    </style>
  </head>
  <body>
    <input required><span>This should be green</span>
    <script>
      document.body.offsetWidth;
      document.getElementsByTagName("input")[0].value = "Test"
    </script>
  </body>
</html>
